Synthesis of substituted 6H-benzo[c]chromenes: a palladium promoted ring closure of diazonium tetrafluoroborates

A highly efficient palladium-catalysed phenyl diazonium tetrafluoroborate participation of C–H activation ring closure protocol has been developed. A series of 6H-benzo[c]chromenes have been synthesized by intramolecular cyclization of ortho diazonium salts tetrafluoroborate of benzyloxyphenyl (Method A), or phenoxymethyl phenyl (Method B). The transformation allows the synthesis of 6H-benzo[c]chromenes with a wide variety of functional groups and substitution patterns from simple and easily accessible precursors.